This invention relates to a power operational amplifier for audio applications, as may be useful in stereo apparatus, amplified cabinet speaker systems, or high-performance TV stereo sets. In particular, this invention relates to an integrated power operational amplifier adapted for parallel clustering with a number of similar amplifiers in order to provide very high output power levels.
To enable a number of operational amplifiers to be used in parallel for driving a common load, it has hitherto been necessary to connect ballast resistors between the outputs of each amplifier and the load, to equalize the currents from each amplifier. An example of such an arrangement is shown in FIG. 1. FIG. 1 shows an amplifier bridge system wherein a load 23 is powered from two pairs of operational amplifiers 1, 2 and 3, 4. Each operational amplifier 1-4 has a ballast resistor Rb placed between the output and the load 23.
The inclusion of such resistors Rb is made necessary by the large cross-conduction currents brought about by the low output impedance of the operational amplifiers 1-4, together with the presence of gain offset or mismatch, which currents would be circulated among the outputs of the operational amplifiers 1-4. Use of ballast resistors Rb results in less power being delivered to the load 23 and more power being dissipated, as well as increasing the cost and size of the system. Low resistance, high-precision power resistors Rb, usually resistance wires, must be employed. These resistors Rb tend to be bulky and significantly expensive.
In one aspect, this invention provides an integrated power operational amplifier adapted for parallel clustering, such that a number of similar amplifiers can be connected in parallel without requiring ballast resistors, thereby delivering a high output power with less unnecessary power dissipation.
In one aspect, this invention provides an integrated power operational amplifier which can alternatively be operated in a master mode or a slave mode, whereby a master amplifier can be connected in parallel with one or more slave amplifiers. This system enables very low impedance loads to be driven, and heat dissipation to be spread over several chips, thereby overcoming the limitations to maximum dissipation which affect prior integrated power systems.
In another aspect, by eliminating the ballast resistors, this invention can deliver more power and dissipate less of it, for the same supply voltage.
The features and advantages of the circuit according to the invention will be apparent from the following detailed description of embodiments thereof, shown by way of non-limitative examples in the accompanying drawings.